Circuit interrupter

ABSTRACT

A circuit interrupter has a pair of contacts, a self-restoring type current limiting element and a first electromagnetic trip device serially interconnected. The current limiting element is connected across a parallel connected resistor and a second electromagnetic trip device. Both trip devices have a common magnetic circuit including a single stationary core and a single movable iron piece. The first trip device responds to a shortcircuiting current flowing through it to open the contacts but the second trip device is operative to open the contacts only after the current limiting element has performed the operation of limiting a shortcircuiting current.

BACKGROUND OF THE INVENTION

This invention relates to improvements in a circuit interrupterincluding a self-restoring type current limiting device.

In circuit interrupters including a conventional self-restoring typecurrent limiting device, it has been already proposed to connect aresistor across the current limiting device in order to reduce theseverity of the overload imposed upon the latter. If the currentlimiting device were to be operated with a current below its thresholdcurrent due to some fault, there might be a danger that the resistorconnected across the device would be burnt out.

Accordingly it is an object of the present invention to overcome theproblem of the prior art circuit interrupters as above described by theprovision of safety means for the abovementioned resistor connectedacross the self-restoring type current limiting device of circuitinterrupters.

It is another object of the present invention to provide a new andimproved circuit interrupter comprising a self-restoring type currentlimiting device and means for preventing flashover from occurring in thecircuit interrupter upon interrupting a short-circuiting current.

SUMMARY OF THE INVENTION

The present invention provides a circuit interrupter comprising, incombination, at least one pair of relatively separable contacts, aself-restoring type current limiting element and first electromagnetictrip means connected in series circuit relationship with the contacts, aresistor connected across the self-restoring type current limitingelement, and second electromagnetic trip means connected in a circuitwith the resistor, the first and second electromagnetic trip means beingoperative independently to trip the contacts, the second electromagnetictrip means being operative only in response to the operation of theself-restoring type current limiting element.

Preferably the first and second electromagnetic trip means includes acommon magnetic circuit including a single stationary iron core and asingle movable iron piece.

In order to prevent the occurrence of flashover upon interrupting ashortcircuiting current, the self-restoring type current limitingelement along with the parallel resistor may be connected to aninterrupting unit including the contacts and the first electromagnetictrip means outside thereof so that the second electromagnetic tripdevice is connected to the contacts without the resistor beinginterposed therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more readily apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a schematic circuit diagram of a circuit interrupterconstructed in accordance with the principles of the prior art;

FIG. 2 is a schematic circuit diagram of a circuit interrupterconstructed in accordance with the principles of the present invention;

FIG. 3 is a graph illustrating the characteristics of the arrangementshown in FIG. 2;

FIG. 4a is a schematic side elevational view of one portion of a circuitinterrupter actually embodying the circuit configuration shown in FIG.2;

FIG. 4b is a schematic plan view of the arrangement shown in FIG. 4a;

FIG. 5 is a view similar to FIG. 4a but illustrating a modification ofthe arrangement shown in FIGS. 4a and 4b;

FIG. 6 is a view similar to FIG. 4a but illustrating anothermodification of the arrangement shown in FIGS. 4a and 4b;

FIG. 7 is a schematic side elevational view, partly in section, of oneportion of another circuit interrupter actually embodying the circuitconfiguration shown in FIG. 2;

FIG. 8 is a sectional view taken along the line VIII--VIII of FIG. 7;

FIG. 9 is a schematic circuit diagram useful in explaining improvementsin the arrangement shown in FIG. 2;

FIG. 10 is a schematic side elevational view, partly in section, of aconventional interrupter illustrating the internal structure thereof;

FIGS. 11 and 12 are schematic circuit diagrams of circuit interruptersincluding further improvements in the arrangement shown in FIG. 2;

FIG. 13 is a side elevational view, partly in section, of a circuitinterrupter actually embodying the circuit configuration shown in FIG.11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings and FIG. 1 in particular, there isillustrated a conventional circuit interrupter including aself-restoring type current limiting element. The arrangementillustrated comprises a pair of terminals 10 and 12, a pair ofrelatively separable contacts 14 connected to one of the terminals, inthis case, the terminal 10, and a thermally responsive trip device 16connected to an electromagnetic trip device 18 subsequently connected tothe other terminal 12. The trip devices 16 and 18 have well knownconstructions. Connected between the set of contacts 14 and thethermally responsive trip device 16 is a resistor 20 having connectedthereacross a self-restoring type current limiting element 22 which maybe simply called a "current limiting element" hereinafter. As disclosedand claimed in Japanese patent publication No. 10,643/1962, aself-restoring type current limiting element includes an amount of aself-restoring type current limiting material in the form of a solid ora liquid at room temperature, for example, sodium or potassiumresponsive to a flow of shortcircuiting current therethrough to beevaporated to present a high resistance to the shortcircuiting currentthereby to limit the current. Thereafter the evaporated material isreturned to its original solid or liquid state to restore the electricconductivity.

In operation, a flow of high shortcircuiting current through the circuitinterrupter causes the current limiting element 22 to be evaporated topresent a high resistance to the shortcircuiting current to limit thecurrent while at the same time commutating the current into the resistor20. The resistor 20 permits the commutated current having a magnitude asdetermined by the magnitude of resistance thereof to flow into the tripdevices 16 and 18 so that the electromagnetic trip device 18 opens thecontacts 14 to trip the circuit interrupter to its open position.

If, due to some fault, the current limiting element 22 were to beoperated with a low current less than a threshold current below whichthe element would not be operated then this might cause a danger thatthe resistor 20 connected across the current limiting element 22 isburnt out. More specifically, the current limiting element 22 has anamount of a self-restoring type current limiting material such as sodiumor potassium sealed under a high pressure therein through a pressurizedgas or spring means or the like. If the pressure on the current limitingmaterial decreases due to leakage of the gas or damage to the springmeans then the operating current thereof is abruptly reduced inmagnitude. Under these circumstances, if the operating current thusreduced flows through the circuit interrupter then the current limitingelement 22 limits the current to cause the current to flow through theresistor 20 in parallel thereto. In that event, the electromagnetic tripdevice 18 is not brought into operation and instead the thermallyresponsive trip device 16 is actuated to trip the circuit interrupter toits open position. In the meanwhile the resistor 20 may be burnt out.

The interrupting operation performed by the arrangement as shown in FIG.1 will now be described in more detail with reference to FIG. 3 whereincurrents flowing through various components of the circuit interrupterare plotted on the abscissa against time on the ordinate. If a currenthaving a magnitude of i₁ flows through the circuit interrupter, then thethermally responsive trip device 16 senses that current to open thecontacts 14 at a time point of t₁ as shown by curve a depicting theinterrupting characteristic exhibited by the circuit interrupterincluding both the thermally responsive trip device 16 and theelectromagnetic trip device 18. If a current in excess of a magnitude ofi₄ flows through the circuit interrupter then the electromagnetic tripdevice 18 quickly senses that current before the thermally responsivetrip device 16 senses it.

Curve c shown in FIG. 3 describes the current limiting characteristic ofthe current limiting element 22 illustrating the relationship betweenthe current flowing through the element 22 and a time point where theelement 22 is initiated to limit that current. For example, if a currenthaving a magnitude of i₁ flows through the current limiting element thenthe latter is initiated to limit the current at a time point of t₂. Thecurrent limiting element 22 is generally responsive to a flow of currenttherethrough having a magnitude equal to or higher than the magnituderepresented by a point of intersection of curves a and c, i.e. greaterthan i₂, to be actuated to limit the current before the associatedcontacts are opened.

FIG. 3 further shows curve labelled b depicting the current limitingcharacteristic of the current limiting element 22 after the magnitude ofa current at which the element 22 is initiated to limit the current hasbeen decreased due to an accidental fault such as previously described.For example, if a current having a magnitude of i₃ flows through thecircuit interrupter then the current limiting element 22 is initiated tolimit the current after the lapse of a time interval of t₃ to commutatethe current into the resistor 20 connected in parallel thereto. Thecommutated current is limited to a magnitude as determined by themagnitude of resistance 14 while it flows through both trip devices 16and 18. Under these circumstances, the electromagnetic trip device 18remains inoperative so that the current continues to flow through thethermally responsive trip device 16 until a time point t₄ at which thethermally responsive trip device 16 is operated in response to thatcurrent to trip the circuit interrupter to its open position.

The resistor 20 connected across the current limiting element 22 hasbeen originally designed and constructed such that a current ispermitted to flow through the resistor for an extremely short timeinterval until the electromagnetic trip device 18 is actuated. Thereforeit is apparent that, when a current having a magnitude of i₃ equal toseveral times, for example, 4.5 times the rated current of the circuitinterrupter continues to flow through the resistor 20 for a long timeinterval up to the time point t₄, this will result in the burning out ofthe resistor 22.

The present invention contemplates the provision of means capable ofbeing called a safety device ensuring that the resistor 20 is preventedfrom being burned out due to a decrease in a current at which thecurrent limiting element is initiated to perform the current limitingoperation.

Referring now to FIG. 2 wherein like reference numerals designate thecomponents identical to those shown in FIG. 1, there is illustrated in aschematic circuit diagram, a circuit interrupter constructed inaccordance with the principles of the present invention. The arrangementillustrated is substantially similar to that shown in FIG. 1 exceptingthat in FIG. 2, the current limiting element 22 has connectedthereacross a series combination of the resistor 20 and anotherelectromagnetic trip device 24. The electromagnetic trip device 24called a "second" electromagnetic trip device is adapted to perform thetrip operation with a current less than the current to which theelectromagnetic trip device 18 called a "first" electromagnetic tripdevice is responsive to trip the circuit interrupter, and immediatelyafter the current limiting element 20 has performed the operation oflimiting a high current such as a shortcircuiting current. Theelectromagnetic trip device 24 is called an "on-limitationelectromagnetic trip device" hereinafter.

Upon a flow of shortcircuiting current through the arrangement of FIG. 2the magnitude of which is insufficient to actuate the current limitingelement 22, the electromagnetic trip device 18 performs the tripoperation as in the normal mode of operation. The on-limitationelectromagnetic trip device 24 is designed and constructed such that,upon a flow of high shortcircuiting current through the arrangement ofFIG. 2 sufficient to operate the current limiting element 22, it isresponsive to a current flowing through the resistor 20 to beimmediately operated to trip the interrupter to its open position. Thisensures that the resistor 20 in parallel to the current limiting element22 is prevented from being burned out. With the current limiting element22 maintained properly operative, it is to be understood that a flow ofhigh shortcircuiting current through the arrangement of FIG. 2 resultsin the actuation of either one of the electromagnetic trip devices 18and 24.

Both electromagnetic trip devices 18 and 24 may be formed into separatestructures which are in turn operatively coupled to a toggle mechanismdisposed in the circuit interrupter. This measure is disadvantageous inthat the resulting circuit interrupter becomes large-sized. Thereforeboth trip devices can be preferably formed into a unitary structure suchas shown in FIG. 4.

As shown in FIG. 4, both electromagnetic trip devices have respectivewindings inductively disposed around a single stationary iron core 26.The windings are designated by the same reference numerals as theassociated electromagnetic trip devices. That is, the windings 18 and 24are provided for the trip devices 18 and 24 respectively. The iron core26 is provided at the opposite ends with a pair of magnetic pole pieces28 and 30 in the form of rectangular plates. One of the pole pieces, inthis case the upper pole piece 30, has one side portion jutting beyondthe other pole piece and a movable iron piece 32 is pivotably mountedthereon. A spring 34 has one end anchored to the movable iron pieces 32and the other end to the end of the jutting side portion of the polepiece 30 to normally bias the movable iron piece 32 away from the lowerpole piece 28 to form an air gap 36 therebetween. The movable iron piece32 normally abuts against a stop 38 attached to the end of the juttingside portion of the upper pole piece 30. The components 26, 30, 32, 36and 26 form a magnetic circuit common to both electromagnetic tripdevices 18 and 24.

With a current in excess of a predetermined magnitude flowing througheither one of the electromagnetic trip devices or their windings 18 and24, the movable iron piece 32 is attracted by the lower pole piece 28.During this attraction thereof the movable iron piece 32 actuates a triplever (not shown) disposed in the circuit interrupter to open thecontacts 14 (see FIG. 2).

The construction by which both electromagnetic trip devices 18 and 24have the common stationary iron core 26 and the single movable ironpiece 32 is advantageous as compared with that in which the cores areprovided independently of each other but it is required to make theoperating current for the on-limitation electromagnetic trip device 24lower than that for the electromagnetic trip device 24. To this end, thewinding 18 may be given an increased number of turns, on the one handand it is preferable to decrease the dimension of the on-limitationelectromagnetic trip device itself, on the other hand. Therefore theon-limitation electromagnetic trip device 24 has a limit as to theincrease in the number of turns of its winding.

Under these circumstances, both electromagnetic devices 18 and 24 can bepreferably constructed as shown in FIG. 5 or 6 wherein like referencenumerals designate the components identical or similar to those shown inFIGS. 4a and 4b.

In FIG. 5, the first electromagnetic trip device has the winding 18thereof inductively disposed around the stationary iron core 26 alonewhile the second or on-limitation electromagnetic trip device has thewinding 24 thereof inductively disposed around both the iron core 26 anda magnetic shunt plate 40 extending between the lower and upper polepieces 28 and 30 respectively. The magnetic shunt plate 40 includes oneportion in contact with that portion of the iron core 26 forming an ironcore for the trip device 24 and the other portion spaced from that coreportion forming an iron core for the trip device 18.

In FIG. 6, the magnetic shunt plate 40 is disposed in spaced parallelrelationship with the stationary iron core 26 between the magnetic polepieces 28 and 30. Then the first electromagnetic trip device has thewinding 18 thereof inductively disposed around the magnetic shunt plate40 while the on-limitation electromagnetic trip device has the winding24 thereof inductively disposed around the iron core 26.

In other respects, the arrangement as shown in each of FIGS. 5 and 6 isidentical in construction to that illustrated in FIGS. 4a and 4b.

In the arrangements as shown in FIGS. 5 and 6, the magnetic fluxresulting from the electromagnetic trip device 18 flows partly through aclosed loop including the iron core 26, the pole piece 30, the movableiron piece 32, the air gap 36 and the pole piece 28. The remainingportion of the magnetic flux flows through the magnetic shunt plate 40and can form the greater part thereof. Under these circumstances, theforce exerted by the spring 34 is decreased. As a result, the operatingcurrent for the electromagnetic trip device 18 can be equal to thatrequired for the arrangement as shown in FIG. 1 while the on-limitationelectromagnetic trip device can operate on a decreased operating currentwithout the necessity of increasing greatly the number of turns of thewinding thereof.

In summary, the present invention comprises a resistor connected acrossa self-restoring type current limiting element and an on-limitationelectromagnetic trip device serially connected with the resistor acrossthe current limiting element and having a smaller operating current thana normal electromagnetic trip device. Thus even if the self-restoringtype current limiting element, operates unusually thereby limiting thecurrent below its threshold current due to some accidental fault, thepresent circuit interrupter operates safely.

Also the electromagnetic trip device 18 and the on-limitationelectromagnetic trip device 24 include the common stationary iron core26 and the associated movable iron piece 32. Furthermore, the stationaryiron core 26 can be operatively associated with the magnetic shunt plate40. Therefore the operating characteristics can readily be compromisedbetween both trip devices resulting in circuit interrupters which aresmall-sized and inexpensive.

Referring now to FIGS. 7 and 8 wherein like reference numerals designatethe components corresponding or similar to those shown in FIGS. 4a and4b, there is illustrated another embodiment of the present invention.The arrangement illustrated comprises a single stationary iron core 26,a first winding 18a-18b inductively disposed around the iron core 26,and a second winding 24 inductively disposed around the iron core 26.The first winding is provided for the electromagnetic trip device 18 andis formed of a main conductor 18a and a shunt conductor 18b electricallyinsulated from each other and disposed in juxtaposed relationship withthe iron core 26 therebetween. The second winding is provided for theon-limitation electromagnetic trip device 24 and includes severalconvolutions wound around the iron core 26.

A combined pole piece and yoke member 30 having an L shape is attachedto one end of the iron core 26 and a pole piece 28 is attached to theother end of the iron core 26. A movable iron piece 32, a spring 34 anda stop 38 are disposed around the stationary iron core 26 in a similarmanner as above described in conjunction with FIGS. 4a and 4b to form amagnetic circuit including the iron core 26, the L-shaped member 30, themovable iron piece 32, an air gap 36 and a pole piece. However themovable iron piece 32 is adapted to be attracted by the end face of thepole piece 28 rather than by the lateral edge thereof.

As in the arrangement shown in FIGS. 4a and 4b the main windingconductor 18a, the stationary iron core 26, the combined pole piece andyoke member 30, the movable iron piece 32 and the pole piece 28 form theelectromagnetic trip device 18 while the winding 24, the stationary ironcore 26, the L-shaped member 30, the movable iron piece 32 and the polepiece form the on-limitation electromagnetic trip device 24.

In operation a load current flowing through the first winding 18a-18b isdivided into two current portions flowing through the main and shuntconductors 18a and 18b respectively. That current portion flowingthrough the main conductor 18a forms a magnetic flux flowing through theclosed loop magnetic circuit as above described and when the currentportion exceeds a predetermined magnitude, the movable iron piece 32 isattracted by the iron core 26. This causes the contacts 14 (see FIG. 2)to be opened through a tripping mechanism (not shown).

It is to be noted that the current portion flowing through the shuntconductor 18b forms no magnetic flux tending to attract the movable ironpiece 32 by the iron core 26.

By properly selecting the force exerted by the spring 34, theelectromagnetic trip device 18 can be operated with a high current. Inaddition, by properly selecting the number of turns of the secondwinding 24, the on-limitation electromagnetic trip device 24 can beoperated with a low current. In other words, the on-limitationelectromagnetic trip device 24 meets the requirement that it shouldperform the tripping operation with a current considerably less than theoperating current for the electromagnetic trip device 18.

In summary, the embodiment of the present invention as shown in FIGS. 7and 8 includes the first winding for the electromagnetic trip device 18and the second winding for the on-limitation electromagnetic trip device24 inductively disposed around the common stationary iron core with oneportion of a load current flowing through the first winding. Thereforethe on-limitation electromagnetic trip device 24 can operate with asmaller operating current than the electromagnetic trip device 18whereby the arrangement as shown in FIGS. 7 and 8 exhibits the sameadvantages as above described in conjunction with FIGS. 4a and 4b, FIG.5 and FIG. 6.

In addition, the arrangement as shown in FIGS. 7 and 8 is advantageousin that, by changing the ratio of a cross sectional area between themain and shunt conductors, the operating current necessary for operatingthe first electromagnetic trip device can be varied.

Referring now to FIG. 9, there is illustrated an arrangement differentfrom that shown in FIG. 2 only in that in FIG. 9 a toggle mechanism 40is operatively coupled to a pair of contacts 14 between the latter andthe parallel connected self-restoring type current limiting element 22and resistor 20 and the on-limitation electromagnetic trip device 24serially interconnected. It will readily be understood that the contacts14, the combination of components 20, 22 and 24, a thermally responsivetrip device 16 and an electromagnetic trip device 18 may beinterconnected in any desired order as long as they are disposed in aseries circuit relationship. Upon assembling those components into acircuit interrupter, it is preferable to dispose the current limitingelement 22 and the parallel resistor 20 on the rear surface of thecircuit interrupter while disposing both electromagnetic trip devices 18and 24 on a common stationary iron core in order to make the circuitinterrupter small-sized.

As in the arrangement of FIG. 2, a flow of high shortcircuiting currentthrough the arrangement of FIG. 9 can cause the first electromagnetictrip device 18 to trip the circuit interrupter to its open position.Alternatively, the second or on-limitation electromagnetic trip device24 can be operated to trip the interrupter to its open position afterthe current limiting element 22 has performed the operation of limitingthe shortcircuiting current. In each case, the current limiting element22 has a high voltage of L di/dt developed thereacross where Lrepresents an inductance exhibited by the associated circuit includingan electric source, a load etc. and di/dt represents the rate of currentlimitation provided by the current limiting element 22. This highvoltage may cause a danger that any one or more of the associatedcomponents will be subject to a flashover dependent upon the position orpositions thereof relative to the current limiting element 22.

This will now be described with reference to FIG. 10 wherein there isillustrated the internal structure of a circuit interrupter generallyemployed at present. In FIG. 10 like reference numerals designate thecomponents identical to those shown in FIG. 9.

In all circuit interrupters, the contacts 14 are connected to a togglemechanism 40 through the metallic connection as shown in FIG. 10 whichhas a substantially equal electric potential to the toggle mechanism. Inthe arrangement of FIG. 9, the high voltage developed across the currentlimiting element 22 upon limiting a current is applied across thethermally responsive trip device 16 and the contacts 14 or the togglemechanism 40. Also the thermally responsive trip device 16 is disposedin the proximity of the toggle mechanism 40 and an electricallyconductive gaseous fluid at a high temperature is formed around the tripdevice 16 and the toggle mechanism 40 upon limiting a shortcircuitingcurrent. This fluid may cause the occurrence of flashover across thethermally responsive trip device 16 and the toggle mechanism 40.

Further, it is difficult to maintain the thermally responsive tripdevice electrically insulated from the toggle mechanism because the twoare close to each other as above described. Maintaining of the goodinsulating relationship between the thermally responsive trip device andthe toggle mechanism has not been previously accomplished becausecircuit interrupters are required to be constructed so as to besmall-sized and inexpensive.

The present invention also contemplates providing effective means forpreventing flashovers such as above described without the necessity ofmuch change of the arrangement and relative positions of the componentsof the circuit interrupters.

In FIGS. 11 and 12 wherein like reference numerals designate thecomponents identical to those shown in FIG. 9, there are illustratedcircuit interrupters including the flashover preventing means as abovedescribed. In FIG. 11, a self-restoring type current limiting element 22is connected across a series combination of a resistor 20 and anon-limitation electromagnetic trip device 24 to form a current limitingassembly A which is, in turn, connected to one of two terminals, in thiscase the terminal 10. The current limiting assembly A is also connectedto the other terminal 12 through an interrupting unit B. Theinterruptering unit B is formed of a pair of contacts 14, a thermallyresponsive trip device 16 and an electromagnetic trip device 18 seriallyinterconnected in the named order with a toggle mechanism 40 operativelycoupled to the contact pair 14.

The arrangement illustrated in FIG. 12 is different from that shown inFIG. 11 only in that the current limiting assembly A and theinterrupting unit B have their positions reversed.

In both arrangements it is noted that the on-limitation electromagnetictrip device 24 is connected directly to the interrupting unit B withoutthe resistor 20 interposed therebetween.

Either of the arrangements shown in FIGS. 11 and 12 can be actuallyformed into a structure as shown in FIG. 13 wherein like referencenumerals designate the components identical to those shown in FIG. 11 or12.

In the arrangement of FIG. 13, the terminals 10 and 12 are attached to amolder casing 42 of any suitable electrically insulating material andthe resistor 20 and the self-restoring type current limiting element 22are disposed within an electrically insulating casing attached to thebottom of the main body of the circuit interrupter.

With the arrangement of FIG. 13 having the circuit configuration asshown in FIG. 11 or 12, the thermally responsive trip device 16 is atthe same potential as the contacts 14. That is, the toggle mechanism 40is at an equal electric potential to the thermally responsive tripdevice 16. Therefore when a high voltage has been developed across thecurrent limiting element 22 upon limiting a high shortcircuitingcurrent, no flashover occurs across the toggle mechanism 40 and thethermally responsive trip device 16. The high voltage across the currentlimiting element 22 is also applied across the terminal 10 and thecontact pair 14 in the arrangement of FIG. 11 and across the terminal 12and the electromagnetic trip device 18 for the arrangement of FIG. 2.However the high voltage does not result in a flashover occurring acrossthe contact pair and the adjacent component because the molded casing 42can readily electrically insulate either of the contacts 14 from theadjacent component.

Thus it is seen that the circuit interrupter as shown in FIG. 13 canlimit and interrupt shortcircuiting currents with no flashover occurringanywhere therein upon interrupting the shortcircuiting current.

While the present invention has been illustrated and described inconjunction with several preferred embodiments thereof it is to beunderstood that numerous changes and modifications may be resorted towithout departing from the spirit and scope of the present invention.For example, the present invention is equally applicable to circuitinterrupters including a fuse having no self-restoring property ratherthan the self-restoring type current limiting element. Such fuses arewell known in the art and may be charged with silica sand. Also thepresent invention is applicable to electric apparatus comprising firstand second electromagnetic means having a considerably differentoperating current from each other with satisfactory results.

What we claim is:
 1. A circuit interrupter comprising, in combination,at least one pair of relatively separable contacts, a self-restoringtype current limiting element and a first electromagnetic trip meansconnected in series circuit relationship with said contacts, a resistorconnected across said self-restoring type current limiting element, andsecond electromagnetic trip means connected in a circuit with saidresistor, said first and second electromagnetic trip means beingoperative independently to trip said contacts, said secondelectromagnetic trip means being operative only in response to theoperation of said self-restoring type current limiting element.
 2. Acircuit interrupter as claimed in claim 1 wherein said first and secondelectromagnetic trip means include a common magnetic circuit including asingle stationary iron core and a single movable iron piece.
 3. Acircuit interrupter as claimed in claim 1 wherein said first and secondelectromagnetic trip means include a common stationary iron core and acommon movable iron piece biased to be normally spaced away from saidstationary iron core by means of the action of a single spring, andwherein said first electromagnetic trip means has a winding inductivelydisposed around said stationary iron core and there is provided amagnetic bypath through which one portion of a magnetic flux produced bysaid winding flows.
 4. A circuit interrupter as claimed in claim 1wherein said first and second electromagnetic trip means include acommon stationary iron core and a common movable iron piece biased to benormally spaced away from said stationary iron core by means of theaction of a single spring and wherein said first electromagnetic tripmeans has a winding formed of a main conductor and a shunt conductordisposed in juxtaposed relationship with said stationary iron coretherebetween, said shunt conductor having one portion of a load currentflowing therethrough.
 5. A circuit interrupter as claimed in claim 1wherein said self-restoring type current limiting element along withsaid parallel resistor is connected to an interrupting unit includingsaid contacts and said first electromagnetic trip means outside thereof.